One of the biggest mistakes I see on the common application is the order of activities. Your activities should be listed in order of importance to you, starting with the most important and moving down to the least important.
There are instructions for this on the side of the activities page but many students seem to be missing that instruction.
That being said, I do sometimes have to suggest that students modify the order of their activities even if they have listed them in their order of importance. You need to keep in mind in ordering the activities what sort of things are important to BS/MD programs.
Yes, you may really enjoy singing, but unless you have won a number of awards for your singing, it probably should not be the first listed activity. On the other hand, several years ago I had a student that was an internationally recognized violinist. In a case like that, putting music first was not a problem.
Just use your best judgement in arranging the activities remembering that volunteering, research and doctor shadowing are some of the important things that BS/MD programs are looking for.